1. Field of the Invention
The present invention relates to a receiver such as a television receiver to be installed on a car and a portable television receiver, which is provided with an auto-tuning system depending on a frequency synthesizer system or a voltage synthesizer system.
2. Description of the Related Art
An auto-tuning system has been known which automatically tunes in to a broadcasting station depending on a frequency synthesizer system or a voltage synthesizer system. The voltage synthesizer system is disclosed, for example, in U.S. Pat. No. 4,398,303. Also, the frequency synthesizer system is disclosed in U.S. Pat. No. 4,317,227.
The above conventional auto-tuning system automatically searches for broadcasting stations by operation of an "up/down" key, which designates tuning direction (i.e., which instructs to tune in to a higher or lower frequency station), to tune in to a broadcasting station of a higher or a lower frequency than the frequency of the presently tuned-in broadcasting station. Further, when broadcasting stations are previously set to corresponding channel keys, for example, a first broadcasting station is preset to a channel key 1, a second broadcasting station is preset to a channel key 2 and so on, the auto-tuning system can tune in to a desired broadcasting station at one touch operation of the channel key.
In recent, portable liquid crystal display television receivers and automobile television receivers (a television receiver installed in an automobile) have been used widely. These television receivers are not used at a fixed area, but are moved to and used at various locations. As the television receiver is moved, broadcasting stations which can be received by the receiver are changed and the signal receiving intensity of a radio frequency received by the television receiver varies. The conventional auto-tuning systems will encounter the above troubles, they therefore can not be used effectively.
Even though particular television stations are preset to the auto-tuning system, the television station can not be received when a television receiver having the auto-tuning system is moved to some other location. Even if the television receiver is moved within a limited area, television stations which can be received will change because mountains and buildings can be obstacles to receipt of radio frequencies.
There are some television stations in cities through out the country, which constitute respective television networks and function as key stations for providing broadcasting services within their own particular service areas.
Most of conventional television receivers indicate only a channel number on the displays during tuning operation. Therefore, when a user of the conventional television receiver travels or goes on business to other place, it is almost impossible for the user to know from his (or her) television receiver how many television stations are providing services in the area, what television channels are assigned to the respective television stations, and what television station constitutes the television network which is familiar to the user at the residence area. The conventional television receiver gives the user much trouble that demands him to do time consuming work for searching for a desired television channel.